The present invention relates to a one-component toner for use with a development unit in which a toner thin layer is formed on a toner transportation member, and more particularly to a one-component positive charging red toner for use with a development unit provided with a toner transportation member and a toner layer thickness regulating device which may flexibly come into contact with the toner transportation member.
Recently, a demand for an electrophotographic copying system capable of making multi-colored copies from multi-colored originals is increasing. This is because multi-colored copies with many colors in addition to a black color are readily understandable when tables, graphs and figures are copied, and more information can be included as compared with mono-chrome copies.
As a coloring agent for use in color toners except a black toner, in particular, for use in red toners, rhodamine-type pigments and quinacridone-type pigments (as disclosed in Japanese Laid-Open Patent Application No. 51-144625) and mono-azo pigments (as disclosed in Japanese Laid-Open Patent Application No. 56-140357) are proposed. These pigments, however, are not capable of yielding a satisfactory red color tone and are not suitable for use in the toner designed to have stable positive charging properties.
When a conventional red color toner for developing latent electrostatic images is used in a development unit provided with a toner layer thickness regulating device, a sufficient positive charge cannot be maintained in the toner and the background of the copies is apt to be conspicuously deposited with the toner, so that it is difficult to obtain clear images.
Furthermore, since a conventional polarity controlling agent for positive charging is usually black or nearly black in color, pure red images cannot be obtained even if a small amount of such polarity agent is contained in the red toner.